This invention relates to coupling for tubing and in particular, to a new and improved coupling especially adapted for use with relatively large diameter rigid tubing of the type used for fuel lines in aircraft and the like.
Typically the couplings are intended for use with tubing of a diameter in the range of 1/2 to 6 inches. The tubing itself normally is rigid and it is a requirement that the coupling provide for relative motion between the lengths of joined tubing including axial translation, rotation and bending. Many installations also require electrical bonding between the lengths of tubing across the coupling.
Flexible couplings have been used for rigid fuel lines in aircraft for many years. A typical coupling is shown in U.S. Pat. No. 3,753,205. This coupling utilizes interengaging threaded members which axially compress the elastomer seals. Also, electrical bonding is provided by electrical pigtails fixed at each tubing end, with the pigtails joined by bolt and nut. An improvement on this coupling is shown in U.S. Pat. No. 3,891,291 which also uses interengaging threaded members for providing axial compression on the O-ring seals. A split ring is positioned about the tubing ends between the O-ring seals and carries a corrugated leaf spring for electrical contact with the tubing ends.
An alternative construction is shown in U.S. Pat. No. 3,186,739. This coupling utilizes interengaging threaded members for holding the coupling ends together, with the O-ring seals positioned in outwardly facing grooves of specific configuration, with one of the threaded members positioned about and engaging both seals. No provision is made for electrical bonding across the tubing ends. A variation on this construction has been proposed utilizing a band over the annular seals and a split ring over the band for holding the band and the tubing ends in position, with the split ring held in place by a spring clip.
These prior art couplings utilize a number of loose parts and the threaded units require two hands for assembly. The threaded units are relatively heavy and in the larger diameters become difficult to assemble.
Accordingly, it is an object of the present invention to provide a new and improved coupling which is relatively light in weight, simple in design and readily assembled with one hand. The latter is a significant feature in present day aircraft where fuel tanks are installed in the thin wing structures. A further object is to provide such a coupling which inherently provides electrical bonding and which automatically locks when assembled, without requiring a separate bonding wire or connection or a separate lock wire.